Cross-country ski

ABSTRACT

This cross-country ski is more particularly intended for the technique termed &#34;skating&#34;. 
     Its bearing length L P , corresponding to the developed length of the sole separating the two respective front (5) and rear (6) contact lines of the ski is at most equal to 1,430 mm. 
     The variation in the deflexion C at the support face under a load of 40 kilograms exerted at the midpoint of said bearing length L P , when the ski is placed on two supports (7,8) which are separated from each other by a length L defined as being equal to the ratio of the bearing length L P  to a constant coefficient equal to 2.78, the supports (7,8) being centerd with respect to the mid-point of the bearing length. The deflection is at most equal to two millimeters, this variation in the deflexion being defined with respect to the deflexion of the ski in the absence of load, itself measured with respect to the plane P passing through the two support points (7,8).

The invention relates to a cross-country ski, and more specifically to across-country ski intended to be used according to the technique termed"skating".

Essentially two techniques are currently known for the practice ofcross-country skiing, each linked with the technique of forwardmovement.

The first, classical, technique, known by the term "alternating steps",consists of thrusting each ski alternately forward in two paralleltracks made for this purpose on the run. The ski used for the practiceof this technique has a central part which is arched, in particular atthe support face, including a region called a "wax chamber" made at thesupport face. This region is intended to receive wax which hasproperties of adhesion to snow. As a result of the thrust exerted by theskier, the chamber comes into contact with the snow and causes thenecessary holding to advance the ski. In view of the fact that the skisare guided in parallel lines made in the snow and in view of the largerange of movement of the ski inherent with the actual alternate-steptechnique, the skis are provided with a relatively high tip which isintended to prevent any risk of the ski sticking into the snow.

There are also types of skis in which the wax chamber is replaced withsole scales, which have asperities pointing backward that preventbackward movement of the ski.

The second technique, which has emerged recently and is moresports-oriented, is called "skating". According to this technique, theskier moves by pointing his skis outward with respect to the directionof forward movement, the propulsion being provided by the alternateexertion of transverse thrusts by the skier on one of his skis. Thistechnique is essentially broken down into four successive phases,respectively a first phase in which the ski is pressing on the outside,followed by a flat gliding phase, followed in turn by a phase ofthrusting on the inner face, and finally by a so-called "flight" phase,during which the ski leaves the snow until the pressure of the followingmovement.

In such a ski, the wax chamber or any other system capable of providingadhesion, even point adhesion, is no longer necessary since the push isno longer exerted in the longitudinal direction but rather by means ofsuccessive and alternate transverse pressure.

In fact, skating skis require high characteristics of strength inlateral flexion and in torsion, in view of the stresses to which theyare subjected. Moreover, with a ski which is too flexible, there is arisk that it will slip as a result of the pressure generated by theskier. The other fundamental element for such a ski concerns its balancewith respect to the foot of the skier, in order not to hamper the flightphase which immediately follows the thrust.

Although skating skis currently available have a satisfactoryperformance level, they nevertheless have certain drawbacks, They mayhave a certain lack of maneuverability, especially during the flightphase. Furthermore, they may have relative bulkiness, caused by theprinciple of divergent foward movement, which may lead to crossing tipsin narrow runs, or with respect to obstacles, rocks, trees, etc. lyingalong the run. Further still, some skis may be difficult to bring backduring the flight phase since they generate wind resistance which isless and less negligible as the ski becomes longer, which, in turndetrimentally affect the "efficiency" and effectiveness of thistechnique. Finally, the so-called skating technique is relativelydifficult to learn.

The object of the invention is to provide a cross-country ski for useaccording to the skating technique which overcomes all these drawbacks.

In order to achieve these results, the invention provides across-country ski which is both less bulky and has the appropriatetechnical characteristics.

SUMMARY OF THE INVENTION

The cross-country ski according to the invention, particularly intendedfor the technique termed "skating", is characterized in that its bearinglength, corresponding to the developed length of the sole separating thetwo respective front and rear contact lines of the ski is at most equalto 1,430 mm, and in that the variation in the deflexion at the supportface under a load of 40 kilograms exerted at the mid-point of saidbearing length, when the ski is placed on two supports which areseparated from each other by a length L defined as being equal to theratio of the bearing length to a constant coefficient equal to 2.78,said supports being centred with respect to the mid-point of the bearinglength, is at most equal to two millimeters, this variation in thedeflexion being defined with respect to the deflexion of the ski in theabsence of load, itself measured with respect to the plane passingthrough the two support points.

In other words, the invention comprises a ski of reduced length andhigher rigidity, especially of the support face, thus guaranteeing,further to greater maneuverability and smaller bulk, effectiveness, inparticular during the thrust phases, which can enhance the conversion ofthe energy corresponding to the thrust of the skier into actual forwardmovement of the ski. This rigidity is manifested by a small variation inthe deflexion measured at the support face when a load of defined valueis applied, compared to the ski when not subjected to any load.

It has been determined that by using the coefficient 2.78 is it possibleto define the distance L separating the two support points such that themeasured deflexion variation value has meaning, whatever the length ofthe ski.

According to one advantageous characteristic of the invention, the ratioof the variation in the deflexion to the bearing length is at most equalto 0.17%.

According to another advantageous characteristic of the invention, theflattening force of such skating skis, that is to say the force exertedat said mid-point of the bearing length of a ski laid flat on a planesurface, necessary to achieve residual deflexion of 0.3 mm, is at leastequal to 400 newtons. It has thus been observed that, with a ski havingsuch a characteristic, its rigidity is such that the results obtainedboth as regards its skiability and its thrust response are comparablewith the expectations of experts in this technique.

Advantageously, the minimum thickness of the support face at itsthickest point is 23 millimeters.

According to another characteristic of the invention, the ratio of thethickness of the support face at its thickest point to the bearinglength is at least equal to 1.7%.

In order to optimize the characteristics of such a short skating ski,its dimension line, that is to say its developed and projected surfaceis broken down into five essential regions, namely from the heel to thetip:

(i) a first region, of short length, in which the width increases, thusdefining a trapezoidal surface;

(ii) a second region, contiguous to the first region and extendingsubstantially as far as the vicinity of the support face, having aconstant width, thus defining a rectangular surface;

(iii) a third region extending from the support face to the widest pointof the ski, namely the tip, in which the width also increases, defininga trapezoidal surface;

(iv) a fourth region extending from the widest point of the ski as faras the front contact line, in which region the width decreases, and thusconstituting a substantially trapezoidal surface; and

(v) a fifth region extending to the front end of the ski, having a widthwhich decreases to a zero value, thereby defining the tip proper.

BRIEF DESCRIPTION OF THE DRAWINGS

The manner in which the invention may be embodied and the advantageswhich result therefrom will better emerge from the embodiment whichfollows, given by way of indication and without limitation, supported bythe attached figures.

FIG. 1 is a cross-country ski according to the invention positioned ontwo supports, represented in a side view.

FIG. 2 is a similar view to FIG. 1, in which the flattening force hasbeen represented.

FIG. 3 is a schematic representation of the projected developed surfaceof a ski according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically illustrates a cross-country ski (1) in side view,in place on two supports (7,8). In a conventional manner, this ski (1)includes a tip (2) extending in front of the front contact line (5) ofthe ski (1) and extending upward, and a heel (3) starting from the rearcontact line (6), also extending slightly upward and thus constitutingthe raised heel. The central region of the ski, or support face (4), hasa deflexion labelled by the letter C, with respect to the plane Ppassing through the two support points (7,8), so that, in the absence ofany load, the support face (4) is not in contact with the ground. Thebearing length L_(P) is defined as extending between the two respectivefront (5) and rear (6) contact lines, that is to say that it is thelength of the sole between these two lines. According to the invention,the bearing length of the ski is at most equal to 1,430 millimeters,substantially corresponding to a ski with a length equal to 1,650millimeters.

According to the invention, this short ski is highly rigid at thesupport face. This rigidity is defined by the deformation of the skiwhen subjected to a load of 40 kilograms exerted at the mid-point of thedistance L separating the two support points (7,8). This distance L isdefined as being equal to the ratio of the bearing length L_(P) to thecoefficient 2.78. In addition, these two support points (7,8) arelocated at an equal distance L/2 on the middle of the bearing lengthL_(P). Finally, this deformation is obtained by determining the value ofthe difference in deflexion C at this point with respect to the plane Ppassing through the two support points (7,8), in the absence of a loadand with the 40 kg load respectively. The difference in the valuesobtained does not exceed two millimeters.

The smaller the deformation the more rigid the ski. This rigidity issuitable for the short skis thus obtained, making it possible tooptimize the energy transfer between thrust given by the skier and thepropulsion generated thereby. This ski is further more handleable, inview of the reduced bulk inherent with the actual skating technique, andalso saves time during the flight phase, in view of the decreased windresistance.

According to the present invention, the rigidity of the support face istied to the bearing length L_(P) by fixing the ratio of the differencein the deflexions, respectively in the absence of load and with a 40 kgload, to the bearing length L_(P) at most equal to 0.17%.

Further in accordance with the present invention, the flattening forceF_(MP), that is to say the force which has to be applied at themid-point of the bearing length L_(P) in order to obtain a residualdeflexion ε of 3/10 mm with respect to the plane P' passing through thetwo respective front (5) and rear (6) contact lines is, greater than orequal to 400 newtons.

The rigidity of the support face can be obtained by incorporating in thestructure of the ski elements, or combinations of elements, inparticular fibre or metal reinforcement, and also by increasing thethickness of the ski at the support face. Preferably, the thickness ofthe support face of the ski is linked to the bearing length L_(P) by therelationship ##EQU1##

The minimum thickness of the thickest point of the support face isadvantageously 23 millimeters.

According to the invention, the dimension line of the ski, representedin FIG. 3, satisfies a particular configuration which gives the skihandleability and effectiveness in its forward movement.

This projection of the ski is broken down into five main regions,namely:

(i) the region of the heel (9), the width of which increases from therear end O of the ski to the vicinity of the rear contact line (6),thereby defining a substantially trapezoidal region;

(ii) the region (10), which extends from the region of the heel (9) andcontinues as far as the vicinity of approximately the mid-point of thebearing length L_(P) ; this region has constant width and is thereforesubstantially rectangular;

(iii) the region (11) extending from the preceding region as far as thevicinity of the widest point of the ski, defined in the field by PI; thewidth of this region increases, thereby again defining a trapezoidalarea;

(iv) the region (13) which extends the from preceding region and extendsbetween the PI and the front contact line (5), and in which the width ofthe ski decreases, thereby defining a substantially trapezoidalsurfaces; and

(v) the region (12), which essentially corresponds to the tip, and inwhich the width decreases from the front contact line (5) to a zerovalue, corresponding to the front end of the ski. This region issubstantially triangular.

All the characteristics listed above, given to a short ski whose supportface develops such rigidity, and whose dimensioned line corresponds tothe above description, thus make it possible to facilitate learning theskating technique. In this way, such skis allow adults in particular tolearn a technique which had hitherto been restricted to the initiatedand more particularly to sports persons. For the latter, these skis areparticularly suited for optimizing performance, especially in view ofthe enhanced effectiveness of the energy transfer during thrusts, andtheir greater maneuverability.

We claim:
 1. A cross-country ski, comprising:a sole having a bearinglength L_(P) extending between a front and a rear contact line of saidski; and a support face extending away from said sole and having adeflexion of not more than 2 millimeters under a load of 40 kilograms,exerted at a mid-point of said bearing length L_(P) compared with adeflexion in absence of said load, the deflexion being measured whensaid ski is placed on two supports separated by a length L, equal to aratio L_(P) /2.78, said supports being centered with respect to themid-point of said bearing length L_(P) and the deflexion being definedwith respect to a plane P passing through respective contact pointsbetween said supports and said sole.
 2. A cross-country ski according toclaim 1, wherein a ratio of the variation in the deflexion to thebearing length L_(P) is at most equal to 0.17%.
 3. A cross-country skiaccording to claim 1, wherein a flattening force F_(MP), exerted at saidmid-point of the bearing length L_(P) of the ski resting on a planesurface P' incorporating the front and the rear contact lines, necessaryto achieve deflexion of 0.3 mm, is at least equal to 400 newtons.
 4. Across-country ski according to claim 1, wherein a minimum thickness ofthe support face at its thickest point is 23 millimeters.
 5. Across-country ski according to claim 1, wherein a ratio of the thicknessof the support face at its thickest point to the bearing length L_(P) isat least equal to 1.7%.
 6. A cross-country ski according to claim 1,further comprising:a first region, of short length, extending from arear end O of a heel of said ski, having a width which increases, as faras the vicinity of the rear contact line, thereby defining a trapezoidalsurface; a second region, contiguous to the first region and extendingsubstantially as far as the vicinity of the support face, having aconstant width thereby defining a rectangular surface; a third regionextending from the support face to a widest point PI of the ski, havinga width which also increases, thereby defining a trapezoidal surface; afourth region extending between the widest point PI and the frontcontact line, having a width which decreases, thereby defining asubstantially trapezoidal surface; and a fifth region extending from thefront contact line to a front end of said ski, having a width whichdecreases to a zero value, thereby defining a tip.